1. Technical Field
The present invention relates to a fuel supply method for fuel injection members of a fuel injection device, and a fuel supply system for carrying out the fuel supply method, more specifically, to a fuel supply method for fuel injection members of a fuel injection device of a gas turbine so as to achieve low-NOx operation, and a fuel supply system for carrying out the fuel supply method.
2. Description of the Related Art
There has been a demand in recent years for a fuel injection nozzle for combustors, capable of injecting fuel such that the exhaust gas has a low NOx concentration, owing to the recent progressively growing severity of controls concerning NOx emission imposed on aero and industrial combustors. To achieve low-NOx combustion, the fuel injection nozzle is required to inject fuel such that the mean flame temperature is low and temperature distribution in flames is uniform. Fuel must be mixed with a large amount of air to lower the mean flame temperature and to make temperature distribution in flames uniform.
Although no problem arises in combustion in a combustor while the combustor is operating in high-power setting, combustion becomes unstable while the combustor is operating in low-power or middle-power setting, when fuel is jetted by a conventional fuel injection nozzle N having a single fuel passage 101 as shown in FIG. 4 and the fuel is mixed in a large amount of air for low-NOx combustion.
As shown in FIG. 5, an improved fuel injection system A′ obtained by altering the conventional fuel injection nozzle N has been proposed as a means for avoiding unstable combustion that occurs in the low-power or middle-power setting. The fuel injection system A′ has a plurality of series of swirl vanes 201 which are concentrically arranged in different radial positions, and a plurality of series of fuel injection mechanisms 202 which are concentrically arranged in different radial positions. The operation of the fuel injection mechanisms 202 is regulated according to engine power settings, and the amount of air into which the fuel is mixed is regulated. The fuel injection system A′ is capable of injecting fuel for the so-called staging combustion.
In the previously proposed fuel injection system A′, fuel is supplied to the fuel injection mechanisms 202 through fuel supply pipes 203 extended through the casing of a gas turbine. Consequently, the flow of combustion air is disturbed and turbulences of the flow of combustion air are caused, thereby, combustion air cannot properly supplied to the fuel injection mechanisms 202. There is the possibility that welded joints of the fuel injection mechanisms 202 and the fuel supply pipes 203 are damaged or cracks develop therein due to difference in thermal expansion between the fuel injection mechanisms 202 and the fuel supply pipes 203. Moreover, the fuel supply pipes 203 are obstacles to assembling work for assembling the gas turbine.